In a solid-state image pickup unit such as a CCD (Charge Coupled Device) image sensor and a CMOS (Complementary Metal Oxide Semiconductor) image sensor, the number of photons entering a unit pixel (a solid-state image sensing device) decreases as a pixel size shrinks, and an S/N ratio declines. As represented by, for example, a Bayer array and the like, pixels are divided into red, green, and blue colors by using color filters, and arranged on the same plane. In this technique, for example, light with wavelengths of green and blue is not allowed to pass through a red pixel (a color filter) and thus, a loss of light occurs, and sensitivity drops. In addition, a false color may be generated, because color signals are produced by performing interpolation processing between red, green, and blue pixels.
Thus, a method of obtaining photoelectric conversion signals of three colors with one pixel by laminating three photoelectric conversion sections has been suggested. For example, one of the three photoelectric conversion sections (e.g. the photoelectric conversion section corresponding to green light) is disposed on a silicon substrate, specifically, on the outside of the silicon substrate, and the remaining two (e.g. the photoelectric conversion sections corresponding to red light and blue light) are provided in the inside of the silicon substrate. The photoelectric conversion section on the outside of the silicon substrate includes an organic material, and is provided between a pair of electrodes. On the other hand, the photoelectric conversion section in the inside of the silicon substrate is configured of a photodiode (Photo Diode).
For example, in a solid-state image pickup unit of Japanese Unexamined Patent Application Publication No. 2011-29337 (PTL 1), a photoelectric conversion section including an organic material is provided on one surface of a silicon substrate, and a multilayer structure of a circuit and wiring (hereinafter simply referred to as “wiring layer”) is provided on the other surface of the silicon substrate. In other words, this solid-state image pickup unit is of a so-called backside-illumination type in which a light-receiving surface and a circuit forming surface are disposed opposite each other. When the photoelectric conversion section and the wiring layer are thus disposed, the distance between the photoelectric conversion section on the outside of the silicon substrate and the photoelectric conversion section in the inside of the silicon substrate is short. Since sensitivity of the photoelectric conversion section depends on an F-number of an on-chip lens, reducing the distance between the laminated photoelectric conversion sections of the respective colors makes it possible to suppress unevenness of sensitivity with respect to each other.